The present invention relates to a method of and an apparatus for serrating a steering wheel, and more particularly to a method of and an apparatus for serrating the boss of a steering wheel of an automobile or the like at a constant position to provide for splined engagement with a steering shaft.
One conventional apparatus for serrating the boss of a steering wheel is illustrated in FIG. 1 of the accompanying drawings. As shown in FIG. 1, the boss 4 of a steering wheel 3 is fitted over a jig 2 having a broach insertion hole 1 defined centrally therethrough to hold a smaller metallic boss 6 slidably against the jig 2, the boss 6 being integral with the boss 4 and having a through hole 5 with its inner peripheral surface to be serrated. The jig 2 is positioned by being fitted in a central opening defined in an upper surface of a frame base 8 fixedly mounted on a chuck frame 7 secured to a broaching machine.
A hydraulically actuatable broach chuck 9 is vertically movably disposed in the chuck frame 7. The broach chuck 9 has a broach insertion hole 10 defined therethrough for insertion of a serrating broach (described later on). A broach stopper 11 projects into the broach insertion hole 10, and a plurality of chuck teeth 12 are disposed above the broach stopper 11 for movement into and out of the broach insertion hole 10. The chuck teeth 12 are normally urged to move away from each other by a spring (not shown).
A chuck cover 13 is vertically movably fitted over the broach chuck 9. The chuck cover 13 has a recess 14 defined in its inner surface for receiving the chuck teeth 12 partly therein. The chuck cover 13 is normally urged resiliently to move upwardly by a spring 15 disposed around the broach chuck 9 and engaging the lower end of the chuck cover 13. The chuck cover 13 has a flange 13a in which a bolt 16 is vertically threaded for abutting engagement with a lower surface of the frame base 8.
FIG. 2 shows a serrating broach 17 in the form of a solid cylinder including a cutting region 17a having cutting teeth shaped complementarily to serrations to be formed, a neck region 17b to be held by the chuck teeth 12, and a stopper region 17c larger in diameter than the neck region 17b.
The broach 17 is inserted into the broach insertion hole 10 of the broach chuck 9 through the hole 5 of the boss 6 and the broach insertion hole 1 of the jig 2. The broach 17 inserted in the broach insertion hole 10 has its stopper 17 held against the broach stopper 11 and the neck region 17b facing the chuck teeth 12.
In operation, the broach chuck 9 is lowered a prescribed stroke to cause the chuck cover 13 resiliently biased by the spring 15 to be lifted relatively to the broach chuck 9. Now, the lower edge of the recess 14 of the chuck cover 13 pushes the chuck teeth 12 radially inwardly toward each other to grip the neck region 17b of the broach 17. During this time, the broach chuck 9 and the broach 17 are centered in coaxial alignment with each other, and the boss 6 of the steering wheel 3 slides over the upper surface of the jig 2 into coaxial alignment with the broach chuck 9 and the broach 17.
Then, the broach chuck 9 is lowered and the broach 17 is pulled out through the boss 6 to enable the cutting teeth of the cutting region 17a of the broach 17 to cut serrations on the inner surface of the through hole 5 of the boss 6.
In the above conventional serrating method and apparatus, however, the broach 17 is not positioned angularly about its central axis, i.e., in a direction normal to the axis thereof in serrating the boss 6. Therefore, the serrations formed on the boss of the steering wheel tend to be out of proper positional relationship to a symmetrically central position or neutral position of the steering wheel.
Where the steering wheel is mounted on the steering shaft of an automobile, for example, the neutral position of the steering wheel may not necessarily correspond to the straight-ahead direction of the automobile because the angular orientation of the steering wheel is not in uniform phase with the serrations on the steering wheel boss. For example, if there are 30 teeth or grooves on the serrated inner boss surface, the angle of a pitch or angular spacing between adjacent teeth or grooves is 360.degree.+30=12.degree., and the angular orientation of the steering wheel in its neutral position may be displaced a maximum of 6.degree. from the straight-ahead direction of the automobile.